Mandarin hybrid tree named ‘TDE4’

ABSTRACT

A new mandarin hybrid called “TDE4” is distinguished by production of fruit that combine mid-late season maturity, large fruit size, attractive deep orange rind color and virtual absence of seeds with rich fruit flavor.

Genus and species:

This application is directed to a description of TDE4, which is amandarin orange tree (Citrus reticulata).

BACKGROUND OF THE INVENTION

The pedigree of TDE4 is shown in FIG. 1. In 1973, pollen from Encoremandarin (unpatented to Applicant's knowledge) was applied to stigmas ofa tetraploid (Temple×4N Dancy) hybrid (unpatented to Applicants'knowledge) and the pollinated flowers were bagged to prevent insectpollination. Fruits were collected in winter 1974, seeds extracted fromeach fruit, and each seed was planted. The chromosome number of eachseedling was determined and those identified as triploid seedlings werebudded onto Troyer rootstock. The resulting trees were planted in thefield in Riverside, Calif. in 1976. These trees were evaluated for treevigor, bearing, and seediness, fruit flavor, fruit color, and otherfruit quality traits from bearing until 1985. Five trees were selectedfrom the original population and repropagated by budding onto C-32citrange, C-35 citrange, Troyer citrange, and trifoliate orangerootstocks. Two trees of the selection now called TDE4 were planted inthe field in Riverside in 1987. When they began fruiting (approximatelyin 1990), these trees were evaluated for the same tree and fruit qualitytraits as the original trees. In 1987, the selection now called TDE4 waschosen for additional testing because it combined medium or large fruitsize, low seed number, rich fruit flavor, deep orange rind and fleshcolor, and acceptable peelability. Budwood of this selection was testedfor viruses and other pathogens by the Citrus Clonal Protection Programand virus-free bud source trees were planted in Lindcove Research andExtension Center, Exeter, Calif. in 1991.

Using this virus-free budwood source, additional trees were propagatedand planted at several California locations between 1993 and 1996. Theseincluded one location in the Coachella Valley (the Coachella ValleyAgricultural Research Station-CVARS, 8 trees), Ojai (12 trees ) andSanta Paula (5 trees) in Ventura Co., and two locations in the SanJoaquin Valley, (Lindcove Research and Extension Center, 8 trees, andOrange Cove, 8 trees). These trial plantings provide most of theavailable data on TDE4. Several different rootstocks have been used inthese evaluations, including Carrizo citrange, C35 citrange, Rich 16-6trifoliate, Cleopatra mandarin, and Schaub rough lemon. In general, nomajor effects of these rootstocks on fruit quality of TDE4 wereobserved, and no incompatiblities have been evident, but longevity oftrees on various rootstocks is not known. Effects of rootstocks on treesize are discussed below.

ASEXUAL REPRODUCTION

The plant known as TDE4 was first asexually propagated in 1975 when budswere collected from hybrid seedling 73-45-5 and grafted onto Troyercitrange rootstock in a greenhouse in at the University of California,Riverside, Calif., U.S.A. This tree was grown in a greenhouse and in1976 it was planted in Field 6D, Row 11, Tree 21 at the Citrus ResearchCenter, University of California, Riverside, Calif., U.S.A. Additionalasexual propagation took place in 1986 when buds were collected fromfield tree 6D-11,21 and grafted onto ‘C32’ citrange and trifoliateorange rootstocks. All characteristics of the original tree, and itsfruit, were established and appear to be transmitted through succeedingasexual propagations.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a novel mandarin hybrid having thecharacteristics described and illustrated herein. The hybrid TDE4produces fruit that combine mid-late season maturity, large fruit size,attractive deep orange rind color and virtual absence of seeds with richfruit flavor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the pedigree of TDE4. All cultivars are C. reticulataexcept orange, which is C. sinensis.

FIG. 2 illustrates, clockwise from top left: a nine-year-old tree ofTDE4 on Carrizo rootstock; fruit on tree; branching pattern; flowerbuds; leaves; and shoots.

FIG. 3 illustrates fruit of TDE4 sampled from nine-year-old tree onCarrizo rootstock.

FIG. 4 illustrates the solids:acid ratio of TDE4 at Santa Paula, Calif.over five years. Points plotted are means of all samples collected on agiven date. Solid lines connect means for sampling dates within the sameseason. The dashed line is a liner regression of solids:acid on samplingdate using data from all years. The regression equation and r² value areshown.

FIG. 5 illustrates the solids:acid ratio of TDE4 at Lindcove, Calif.over five years. Points plotted are means of all samples collected on agiven date. Solid lines connect means for sampling dates within the sameseason. The dashed line is a liner regression of solids:acid on samplingdate using data from all years. The regression equation and r² value areshown.

FIG. 6 illustrates the solids:acid ratio of TDE4 at Orange Cove, Calif.over five years. Points plotted are means of all samples collected on agiven date. Solid lines connect means for sampling dates within the sameseason. The dashed line is a liner regression of solids:acid on samplingdate using data from all years. The regression equation and r² value areshown.

FIG. 7 illustrates the solids:acid ratio of TDE4 at Ojai, Calif. overfive years. Points plotted are means of all samples collected on a givendate. Solid lines connect means for sampling dates within the sameseason. The dashed line is a liner regression of solids:acid on samplingdate using data from all years. The regression equation and r² value areshown.

DETAILED DESCRIPTION OF THE INVENTION

All major color code designation are by reference to The R.H.S. ColourChart (2001) provided by The Royal Horticultural Society of GreatBritain.

Eight to ten year-old trees grown in the ground were examined to preparethe description in this and the following paragraph. Tree shape (FIG. 2)is approximately sphereoid, rather similar to that of orange trees. Thetrees have not been noted as particularly susceptible to any diseasesand, based on a freeze in 1999, appeared only slightly more cold hardythan oranges of similar age. Leaves (FIG. 2) are simple, brevipetiolate,lanceolate, with entire or slightly margins. The petiole shape is narrowand linear in shape. In comparison with most old-line citrus cultivars,trees of TDE4 are somewhat thorny, with normal branches having shortlength (4 mm) thorns at about 13% of the nodes, and vigorous sproutshaving short (3 mm) thorns at about 3% nodes. Thorniness will probablydecrease as the cultivar ages.

Flowers of TDE4 are typically hermaphroditic, with Green-White 157Dpetals and yellow 13B anthers (FIG. 2). Trees flower from early Aprilinto May at most locations. Pollen is somewhat sparse, with viability(estimated in an in vitro germination test) of 8%. Pollen tube growth isalso less than that of fertile, diploid mandarins.

The height and spread of a mature (27 years old) TDE4 tree is asfollows: Tree height=6.0 m; Width=6.25 m. Trunk diameter of a 27 yearold tree was 25.6 cm when measured 38 cm above the ground. Trunk colorusing the R.H.S. Colour Chart is Brown N200B.

-   Leaf characteristics of TDE4 trees are as follows:    -   -   Leaf shape.—Ovate.        -   Blade length.—83.6 mm.        -   Blade width.—44.7 mm.        -   Apex description.—Acute with weak emargination.        -   Base description.—Convex.        -   Abaxial leaf color (RHS chart).—Yellow Green 146B.        -   Adaxial leaf color (RHS chart).—Yellow Green 147A.-   Petiole characteristics of TDE4 trees are as follows:    -   -   Petiole length.—11.8 mm.        -   Petiole width.—2.0 mm.        -   Petiole color (RHS chart).—Yellow Green 147A.

If sufficient fruit was available, 10-fruit samples were collected fromeach location two or three times each year beginning in 1997 or 1998.Generally samples were collected from two or three trees per location oneach sampling date. These fruit were evaluated in Riverside for a rangeof traits as summarized in Table 1.

TABLE 1 Fruit characteristics of TDE4 averaged over 4 locations and 4seasons. Samples were collected from mid-January to early May at SantaPaula, Ojai, and Lindcove, and from mid-January to mid-March at OrangeCove. “N” indicates the total number of fruit samples analyzed. Resultsare averaged over several rootstocks. The trees examined for Table 1ranged from 3-8 years old and were grown in the ground. Trait N Min MaxMean SD Fruit height (mm) 201 47.5 76.8 58.3 5.29 Fruit width (mm) 20159.6 102.1 74.7 7.15 Fruit height:width 201 0.67 0.91 0.78 0.045 Rindcolor 201 4.5 13.0 12.3 1.04 Rind texture 201 2.3 5.0 3.3 0.57 Neck 2010 2.00 0.23 0.430 Peelability 201 5.00 10.00 8.23 0.850 Rind thickness(mm) 201 3.00 6.00 4.21 0.687 Seeds per fruit 201 0 5.00 0.32 0.696Fruit weight (g) 201 91.0 335.0 174.5 41.94 Juice content (%) 195 18.256.3 42.2 6.91 Soluble solids (%) 195 7.85 19.50 12.31 1.698 Acid (%)195 0.56 2.03 1.13 0.302 Solids:acid 195 5.81 24.60 11.61 3.332^(a)Visual rating on a scale of 0-13; 0 = green, 13 = red-orange^(b)Visual rating on a scale of 1-8; 1 = very smooth, 8 = extremelycoarse ^(c)Visual rating on a scale of 0-3; 0 = no trace of neck, 3 =neck with a diameter at least 50% of fruit diameter ^(d)Subjectiverating of ease of peeling a single fruit; 1 = very difficult, 10 = afruit with completely separated rind and segments. Fruit with ratings of7 or higher would be relatively easy to peel.

Based on this data, TDE4 fruit are oblate in shape (FIG. 3), with littleor no neck. The average fruit size is large for a mandarin (classed asMammoth by California state standards). Rind color is orange-red N30C.The rind texture is somewhat variable, depending on tree age and crop.For older trees with a moderate to heavy crop, rind texture is smooth,with conspicuous oil glands (about 50 cm²). The rind of fruit from treeswith very light crops is sometimes excessively rough or bumpy. The rindis quite easy to peel when fruit are mature, but can be more adherentearly in the season. Fruit flesh color is orange 28A. Flesh thickness isabout 68 mm. Albedo color is Yellow-White 158B. Albedo thickness isabout 2.0 mm. Adherence of rind to pulp is medium or moderate. Thenumber of segments per fruit is 9-10. The fruit base (stalk end) isslightly concave (FIG. 3), and the apex is truncate with a slightdepression in the stylar end and a small (2 mm), usually closed, stylarscar.

Important determinants of maturity date for citrus fruit are thesolids:acid ratio and juice content. Using data for all years, juicecontent show a statistically significant correlation with sampling dateat only at Santa Paula, where the slope of the regression was positive.Regressions were slightly negative at the other three locations, but notsignificantly so. This indicates that at Santa Paula, the site with thelatest maturity date, fruit sampled from mid-January to mid-February hadnot yet reached maturity. At the other locations, juice content showedlittle tendency to decrease later in the season. Solids:acids ratio wassignificantly correlated with sampling date at all location except SantaPaula (FIG. 4). Using these regressions, the estimated dates on whichfruit reached an 8:1 solids:acid ratio was January 2 for Ojai, January15 for Orange Cove, January 16 for Lindcove, and January 27 for SantaPaula.

During the 1999-2000 season, fruit of TDE4 and several other mandarinvarieties were harvested, run over a packline at the University ofCalifornia Lindcove Research and Extension Center, waxed and evaluatedby a taste panel. Evaluations were done before storage, after storagefor 11 days at 68 F, and after storage for 21 days at 37 F. Fruit wererated on a 9 point scale, where a score of 1 is “Dislike extremely”, 5is “Neither dislike or like”, and 9 is “Like extremely”. Fruit weresampled from test plots at Lindcove and Orange Cove on February 23(Table 2) and Mar. 21, 2000 (Table 3). These samples would representmid-late season fruit of TDE4, the fruit from Lindcove and Orange Covehaving solids:acid ratios of 10.8 and 10.5 on February 18 and 15.1 and14.3 on March 14 respectively. TDE4 fruit from the two locations weresimilar in all traits evaluated. Their ratings were good for all traitsbefore storage, and were little changed by storage at room temperatureor at 37 F. TDE4 had higher scores than Gold Nugget and W. Murcott forvisual appeal and similar peelability. It also had slightly higher tastescores in most comparisons.

TABLE 2 Sensory panel evaluation of TDE4 (TDE4L), Gold Nugget, W.Murcott from Lindcove and TDE4 from Orange Cove (TDE4M) harvestedFebruary 22, 2000. Gold W. Storage TDE4L TDE4M Nugget Murcott VisualEvaluation Initial Mean 7.0 7.2 3.6 5.3 SD 1.6 1.4 1.6 1.6 11 days Mean7.2 7.3 6.7 5.3 @ 68 F SD 1.1 1.3 1.2 2.0 21 days Mean 7.2 7.5 6.7 4.2 @37 F SD 1.6 1.7 2.2 1.8 Peelability Evaluation Initial Mean 7.5 6.8 7.26.6 SD 0.8 2.2 1.5 2.1 11 days Mean 6.7 7.2 8.1 7.5 @ 68 F SD 1.6 1.71.3 1.7 21 days Mean 7.1 7.6 8.0 7.0 @ 37 F SD 1.7 1.9 1.8 2.0 TasteEvaluation Initial Mean 7.3 7.2 6.5 6.2 SD 1.1 1.7 1.6 1.9 11 days Mean6.1 5.9 5.5 6.9 @ 68 F SD 2.5 1.9 2.1 2.5 21 days Mean 6.7 6.6 5.7 6.9 @37 F SD 2.1 1.9 1.9 2.1

TABLE 3 Sensory panel evaluation of TDE4 (TDE4L), Gold Nugget, W.Murcott from Lindcove and TDE4 from Orange Cove (TDE4M) harvested March20, 2000. Gold W. Storage TDE4L TDE4M Nugget Murcott Visual EvaluationInitial Mean 6.8 7.1 4.5 6.6 SD 1.6 1.7 1.3 1.4 11 days Mean 6.9 7.4 5.87.3 @ 68 F SD 1.5 1.5 1.2 0.9 21 days Mean 6.8 7.5 6.9 5.3 @ 37 F SD 2.11.1 1.4 2.2 Peelability Evaluation Initial Mean 6.9 7.2 7.7 7.8 SD 1.81.9 1.0 0.9 11 days Mean 6.6 7.3 7.6 7.6 @ 68 F SD 1.6 1.4 1.5 1.3 21days Mean 7.0 7.7 7.8 7.1 @ 37 F SD 1.6 1.2 1.4 1.8 Taste EvaluationInitial Mean 7.5 6.9 7.1 6.8 SD 1.2 1.4 1.7 1.9 11 days Mean 7.0 6.8 6.76.7 @ 68 F SD 2.1 1.3 1.8 1.7 21 days Mean 7.4 6.7 6.3 6.6 @ 37 F SD 1.81.4 1.8 1.7

Yield of TDE4 was evaluated from visual ratings of crop relative to treesize at each location from 1998-99 to 2001-2002. The rating scale rangedfrom 0 (no crop) to 5 (very heavy crop). Crops at Ojai were fairly good,being 2-3.3 during the last three of the four years evaluated. At SantaPaula, crop ratings indicated moderate alternate bearing, with averagevalues of 0.50, 2.60, 0.88, and 2.90 from 1998-99 to 2001-2002respectively. Trees planted at Lindcove in 1994 showed similar behavior,2.94, 1.88, 1.50, and 2.90 from 1998-99 to 2001-2002 respectively. AtOrange Cover, trees showed rather severe alternate bearing with cropratings of 1.88, 4.00, 0.06, and 1.60. Yield at Lindcove in 2000 and2001 was 29 and 14 kg tree, while at Orange Cove it was 66 and 0 kgtree. Trees appear to flower profusely, but fruit set is virtuallyabsent.

Trees that were screened to exclude bees during flowering produced veryfew fruit for two consecutive years, but it is possible that TDE4 isself-fertile but requires pollination for fruit set. As discussed above,tree fruit is set in April and May. First and last harvest dates forRiverside California are estimated as February 15 and May 15. BecauseTDE4 is a mid-late season fruit, it is likely that trees will show afairly strong tendency to alternate bearing, and this is supported bythe data for some locations.

Two siblings of TDE4, “TDE2” and “TDE3,” were compared to TDE2. TDE4 isdistinct from these cultivars in having a smoother rind, intermediatematurity date, and distinctive flavor. TDE4 fruit are more oblate inshape than those of TDE3, and the rind color of TDE4 is deeper orangethan that of TDE2. Trees or fruit of TDE4 can be distinguished fromthose of other mandarins, including TDE2 and TDE3, using simple sequencerepeat (SSR) DNA markers. Using TDE4 DNA as template, PCR primer setTAA3 (F=AGAGAAGAAACATTTGCGGAGC (SEQ ID NO:1), R=GAGATGGGACTTGGTTCATCACG(SEQ ID NO:2)) amplified a band of 145 bp while TDE2 and TDE3 had bothhad two bands of 142 and 145 bp. Primer sets TAA3 plus CAC15(F=TAAATCTCCACTCTGCAAAAGC (SEQ ID NO:3), R=GATAGGAAGCGTCGTAGACCC (SEQ IDNO:4)) and TAA15 (F=GAAAGGGTTACTTGACCAGGC (SEQ ID NO:5),R=CTTCCCAGCTGCACAAGC (SEQ ID NO:6)) distinguished TDE4 from thefollowing cultivars: Dancy, Encore, King, Willowleaf, Wilking, GoldNugget, Pixie, W. Murcott, Ellendale, Hernandina Clementine, Fortune,Kara, Kinnow, Murcott, Nova, and Ponkan.

The seed parent of TDE4 is a tetraploid hybrid between a ‘Temple’ tangorand a tetraploid tree of ‘Dancy’ mandarin. The tetraploid (Temple×4NDancy) parent (referred to below as 4N-TD) was never released by theUniversity of California and only two trees of this variety exist. TDE4is distinct from this variety in having less than 1 seed per fruit while4N-TD averages 10 seeds per fruit. Fruit of 4N-TD have an aspect ratioof about 0.88, mature in December-January and hold on the tree for about1 month, while those of TDE4 have an aspect ratio of about 0.78, maturein February and hold on the tree for 2-3 months. Fruit of 4N-TD havethicker rinds (5.5 mm) than those of TDE4. Trees of 4N-TD are somewhatsmaller (3.8 m tall) than those of TDE4 (5.9 m tall).

The pollen parent of TDE4 is ‘Encore’ mandarin. TDE4 differs from Encorein that Encore fruit average about 20 seeds per fruit while fruit ofTDE4 have less than 1 seed per fruit. Encore fruit mature inMarch—April, about 1 month later than those of TDE4. Encore fruit alwayshave a distinctive green or dark brown spot or blotch on the rind whichis absent on TDE4 fruit. The average size of TDE4 fruit is larger thanthat of Encore. Encore fruit have an aspect ratio of 0.71 and muchthinner rinds (2.0 mm) while those of TDE4 has an aspect ratio of 0.78and rinds 3.5 mm thick. Encore fruit hold extremely well on the tree(4-6 months). The height of mature (35 year old) Encore trees is about4.1 m, shorter than that of mature (27 years old) TDE4 trees.

Vigor of TDE4 trees has varied greatly across locations. At CVARS, wherethe trees grew rapidly, canopy volumes of 7-year-old trees averaged 23.0m³. In contrast, at the cooler Santa Paula and Ojai locations,7-year-old trees averaged 4.3 and 5.6 m³. Trees in the desert locationshave never produced fruit, perhaps contributing to greater vegetativegrowth. Rootstock affected tree size at some locations. At Lindcove andOrange Cove, trees on Carrizo were the largest, followed by C35, andthen Cleo and trifoliate which were similar. At Ojai, the largest treeswere on C35, followed by Schaub rough lemon and Carrizo. At CVARS, treeson Carrizo, C35 and Cleo were similar in size. At Santa Paula, thesingle tree on Carrizo was smallest than that on C35. No evidence ofrootstock-scion incompatibilities was evident.

TDE4 can be propagated on many available citrus rootstocks by budding.To reduce thorniness, budwood should be selected from thornless, uppercanopy branches. Tree spacing in field plantings will depend on vigor ofthe rootstock. For Carrizo citrange rootstocks, a recommended treedensity is about 150 trees per acre. Higher densities are possible, butwill require more frequent pruning or hedging. Care of young treesshould be similar to that used for other mandarins or oranges. Trees canbe grown with pollinizer cultivars such as Minneola, Valencia orange, orunrelated mandarins (not Temple, Dancy, Encore of other TDE hybrids)that produce viable pollen. Optimal pruning practices have not yet beendeveloped, but in many locations trees will perform well with relativelylittle pruning. Maturity dates will vary with location, probablydepending on the number of heat units and soil conditions.

As with some other mandarin, sprays and gibberellic acid may increasefruit set when pollinizers and/or pollinators are inadequate.

TDE4 trees are winter hardy in USDA zones 9b to 11.

1. A new and distinct variety of mandarin hybrid tree havingsubstantially the characteristics described and illustrated herein.